360 Question

I too would start out using the 727, but, I'd also keep the 904 with it's driveshaft and yoke in case I wanted to make the change later. If you can get the van started, do it. That way you can test the transmission and rear end too. If the van has an 8 3/4 in it, you might want to keep that and have it narrowed for your Dart. Chances are your rear end is a 7 1/4 and not the greatest for higher horsepower.